The present invention relates to cementing operations and, more particularly, in certain embodiments, to methods and compositions that comprise cement kiln dust (“CKD”) and rice husk ash.
In cementing methods, such as well construction and remedial cementing, settable compositions are commonly utilized. As used herein, the term “settable composition” refers to a composition(s) that hydraulically sets or otherwise develops compressive strength. Settable compositions may be used in primary cementing operations whereby pipe strings, such as casing and liners, are cemented in well bores. In performing primary cementing, a settable composition may be pumped into an annulus between a subterranean formation and the pipe string disposed in the subterranean formation. The settable composition should set in the annulus, thereby forming an annular sheath of hardened cement (e.g., a cement sheath) that should support and position the pipe string in the well bore and bond the exterior surface of the pipe string to the walls of the well bore. Settable compositions also may be used in remedial cementing methods, such as the placement of cement plugs, and in squeeze cementing for sealing voids in a pipe string, cement sheath, gravel pack, formation, and the like.
Settable compositions used heretofore commonly comprise Portland cement. Portland cement generally is a major component of the cost for the settable compositions. To reduce the cost of such settable compositions, other components may be included in the settable composition in addition to, or in place of, the Portland cement. Such components may include fly ash, slag cement, shale, metakaolin, micro-fine cement, and the like. “Fly ash,” as that term is used herein, refers to the residue from the combustion of powdered or ground coal, wherein the fly ash carried by the flue gases may be recovered, for example, by electrostatic precipitation. “Slag,” as that term is used herein, refers to a granulated, blast furnace by-product formed in the production of cast iron and generally comprises the oxidized impurities found in iron ore. Slag cement generally comprises slag and a base, for example, such as sodium hydroxide, sodium bicarbonate, sodium carbonate, or lime, to produce a settable composition that, when combined with water, may set to form a hardened mass.